The invention relates to a device for connecting piping sections of a pipeline through which a medium flows. The invention contains a number of tension elements disposed so as to be distributed over the circumference of pipe ends of the pipeline. In this case, the expression pipeline refers in particular to a pipeline through which a hot medium, for example steam, under high pressure flows.
On account of the steam parameters to be expected in future power plants, having a steam or live-steam temperature of more than 600xc2x0 C. and a steam pressure of more than 250 bar, correspondingly high demands will be imposed on the pipelines and piping connections. In such a steam feed line, the connecting point between pipe sections of the pipeline carrying steam may be configured to be welded and thus undetachable or may be configured to be detachable like a flange connection. Such connections are also provided between the pipeline and a steam inlet valve of a steam turbine and between the steam inlet valve and the turbine casing. Whereas known detachable connections, on account of the low residual material characteristics of conventional materials related to the temperature, can only be used to a limited extent, welded connections, in particular in the event of an inspection, have disadvantages with regard to ease of assembly and dismantling.
The use of conventional pipe connections like a flanged and screwed pipe joint, a screwed pipe joint by a cap nut or a clamped connection, is problematic at high and maximum steam states for different reasons. The flanged and screwed pipe connection requires the availability of a screw material of sufficient strength. In addition, on account of the round screw cross section, only a limited proportion of the flange surface, i.e. of the space available radially around the pipeline, can be utilized for applying tensile forces. Furthermore, the round supporting surface of the nut requires a minimum distance from adjacent constructional elements, so that a minimum flange outside diameter results from the outside diameter of the pipeline and the minimum distance between adjacent nuts on the pitch circle and also from the outside diameter of the supporting surface. The resulting distance between the pipe outer wall and the center of the screw bolt produces a relatively high flange moment, a factor that constitutes a considerable disadvantage in particular with low available material characteristics.
In a pipe connection using a cap nut, a stress concentration occurs in particular at the transition from the cylindrical region to the axial bearing region. With low material characteristics related to the temperature, a limit in the creep deformations in this region has to be taken into account in the configuration of the cap nut, a factor which leads at high steam states to relatively large components, which can therefore only be handled with difficulty. Since a flange, after the cap nut has been inserted, has to be welded to, for example, the valve to be connected, this has an adverse effect on both the production, when welding correspondingly large wall thicknesses, and on the overall length of the connection. In addition, a relatively large, radial and axial space is required at high temperatures.
The relatively large radial expansions also result in a clamped connection disclosed, for example, by Published, Non-Prosecuted German Patent Applications DE 197 11 580 A1 or by DE 24 52 770 A1, in which a clamped connection of a number of connecting elements in the form of claw-like or clamp-like ring segments are disposed on the circumference of the flange-like connection. In addition, in a flange connection with such connecting elements, there is the disadvantage that the latter do not have sufficient strength to absorb the tensile forces, especially as the connecting elements, as a result of radially surrounding the outsides of the flange, are also subjected to a bending load in addition to a tensile stress.
Specific cooling in the region of such pipe connections between the medium carried by the pipeline and the flange connection is also problematic, since flange cooling requires an additional radial distance between the flange and the pipeline for the cooling medium. In addition, heat losses may occur due to such cooling, and these heat losses, in a steam line, may lead to a loss of working capacity, that is to an energy loss of the medium carried in the pipeline.
It is accordingly an object of the invention to provide a device for connecting piping sections which overcomes the above-mentioned disadvantages of the prior art devices of this general type.
With the foregoing and other objects in view there is provided, in accordance with the invention, a combination of a pipeline having connecting pipes with pipe ends and contact surfaces, with a device for connecting the pipes through which a medium flows. The device contains shaped elements disposed at the pipe ends of the pipes and a number of tension elements disposed distributed over a circumference of the pipe ends of the pipes. Each of the tension elements have a tension shank with ends and extend in a longitudinal direction of the pipes between the shaped elements and the tension elements are disposed adjacent to each other in a circumferential direction of the pipes. Each of the tension elements have shaped parts with one of the shaped parts disposed at each of the ends of the tension shank and the shaped parts extend in a transverse direction of the tension elements. The shaped parts engage in the circumferential direction of the pipes behind the shaped elements at an end remote from the contact surfaces of the pipe ends.
The object is achieved by a number of tension elements. The tension elements extend with their tension shanks in the longitudinal direction of the pipe between shaped elements which are disposed at the pipe ends and are disposed adjacent to each other in the circumferential direction of the pipe. Shaped parts provided at the ends of the tension shank of the respective tension element and extending on both sides of the tension element in its transverse direction engage behind or overlap the shaped elements provided at the pipe ends in the circumferential direction of the pipe preferably in a positive-locking manner.
The connecting device has a plurality of the tension elements preferably disposed so as to be uniformly distributed over the circumference of the piping sections to be connected. The connecting device has at the same time a high strength and also at a high temperature and a high pressure of the medium carried in the pipeline, ensures an especially compact configuration of the connecting elements with especially low radial expansion compared with the known flange connections, in particular compared with the known clamped connections. In addition, stress concentrations as a result of force deflections are reduced. Furthermore, an especially advantageous equilibrium of forces, while avoiding a bending load on the tension elements, is achieved on account of the symmetrical configuration and in particular on account of the symmetrical configuration of the tension and shaped elements.
By the suitable forming of the shaped parts of the tension element or of each tension element and of the shaped elements on the respective pipe end, an especially favorable ratio between tensile cross section of the tension element and the effective areas can be set inside the positive-locking connection.
With regard to the tension elements and their shaped parts and with regard to the shaped elements of the pipe sections, a variant in which the shaped elements are formed by radial projections which are attached to or integrally formed on the respective pipe end and are therefore discrete is especially advantageous. The radial projections may also be produced by incorporating grooves in an annular bead integrally formed on the pipe end. In this variant, the shaped parts preferably integrally formed on the ends of the tensile shank, extending between adjacent projections in the longitudinal direction of the pipe, of the respective tension element are expediently configured like a hammer head. The shaped parts, that are configured in mirror symmetry like an I-girder with regard to the longitudinal axis of the tension element and which therefore project on both sides of the tension element beyond its shank in the transverse direction, engage behind the shaped elements of the respective pipe section in the circumferential direction of the pipe at the end remote from the corresponding pipe orifice.
In an expedient configuration, each pipe end has a pipe wall thickness increasing toward its contact surface, whereas the tension shank of the tension element is channeled on the side facing the pipe ends and is therefore of necked-down or concave configuration. In both embodiments, the tension element has a tension shank extending between the shaped parts and having a ring-segment-like cross-sectional area. However, the cross-sectional area may also be trapezoidal, rectangular, kidney-shaped or hexagonal.
Alternatively, the shaped elements are formed as radial recesses in the pipe wall of the pipe end, the respective pipe end being of correspondingly thick-walled configuration. In this variant the tension elements, the shaped parts of which are inserted into the recesses in a positive-locking manner, are expendiently configured at the end like a double hammer root or a fir-tree root, as is conventional practice in the case of turbine blades. Further types of joining are also conceivable, for example a saw-tooth, a hooked or a dovetailed connection. The respective shaped part of the tension element then has a corresponding number of partial branches lying one behind the other in the longitudinal direction of the pipe and being in engagement in the recess in a parallel configuration and having an outer contour adapted to the contour of the recess, the partial branches in turn projecting in the circumferential direction of the pipe, i.e. extending in the circumferential direction of the pipe. An especially preferred embodiment of this variant is a fir-tree head on the respective end of the tension element.
The tension element itself is advantageously prestressed like a tie rod. This reliably prevents the pipe ends from lifting from one another during pressurizing. To compensate for tolerances and to compensate for operationally induced elongations of the tension elements, shims are expediently provided between the opposite effective areas of the shaped parts, on the one hand, and the shaped elements, on the other hand, at least at one end of the tension element. In this case, the shim or each shim may be produced to oversize. Alternatively or additionally, a spring-back sealing element may also be provided between the pipe ends. The effective areas opposite one another may also be configured to be inclined relative to one another in such a way that the shim is virtually drawn into the groove formed between the effective areas at a distance from one another. In addition, the configuration of an inclined or rising effective area on the shaped element and/or on the shaped part has the advantage that the shaped part of the tension element is held in position during assembly. The tie rods are preferably tightened by a hydraulic device or by thermal elongation.
To avoid stress concentrations as a result of notch effects on the tension shank, extending between the shaped parts, of the tension element, the latter, on its bearing surface facing the pipe ends, has rounded-off-surface edges preferably both in the region of the shaped parts and along the tension shank. Accordingly, the shaped element or each shaped element has surface corners rounded off at the transition to the pipe end and having a rounded portion corresponding to the rounded edge portions of the tension element and having a certain radius of curvature or a combination of radii. On the one hand, this avoids sharp surface edges, which promote notch effects, inside the connection. On the other hand, especially tight bearing of the respective tension element against the outer surface of the pipe ends is possible by a rounded portion of the surface edges and corners having radii adapted to one another.
The tension elements or each tension element may also be disposed at a distance from the pipeline with a defined radial gap. The introduction of heat from the medium carried in the pipeline via the pipe outer surface into the tension element is thus reduced. On account of the heat-transmission resistance between the medium and the tension element, only a comparatively small quantity of heat is to be dissipated here if the tension elements are cooled. This advantageously leads to only a slight reduction in the temperature of the medium in the pipeline. Therefore, each of the tension elements has a heating bore for transmitting heat.
The advantages achieved with the invention consist in particular in the fact that, by the pipe connection formed by the tension elements which are connected in a positive-locking manner to corresponding shaped elements on the pipe ends of piping sections to be connected, especially favorable division of the available circumferential area of the pipeline with at the same time especially high surface utilization is achieved.
Furthermore, due to specific adaptation of the radial extent of the connection and the advantageous division of the available area, especially small deformations of the tension elements and of the pipe ends and thus only slight mechanical stresses inside the connection occur owing to the fact that the tension elements lie in the radial flange grooves or radial grooves formed by the projections or by the recesses, the tension elements bear virtually directly against the pipe outer wall beyond which the shaped elements project on the pipe end side, with the result that the smallest possible radial expansion of the connection is achieved.
Advantageously used as an assembly aid and for fixing are clamping rings which enclose the tension elements and, as a result of the radial force thus produced, hold them in their position.
In accordance with an added feature of the invention, the tension shank has a cross-sectional area shaped like a segment of a circle.
In accordance with another feature of the invention, each of the pipe ends has a contact surface and a pipe wall thickness increases toward the contact surface, and the tension shank is channeled on a side facing the pipe ends.
In accordance with a concomitant feature of the invention, the tension elements have a symmetrical configuration in both a longitudinal direction and a transverse direction.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for connecting piping sections, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.